German 2,238,631 describes a cutter tool with a chip breaker wherein the groove adjacent the cutting edge has at least one raised frustoconical bump. This cutter is used to break easily raised chips. Also in accordance with German 2,309,443 it is suggested to arrange in the chip-breaker groove a plurality of spaced spherical segment chip-breaker projections.
The known cutter inserts are however only usable, because of the arrangement of the chip-forming elements and the geometry of the chip-breaker groove, in a limited range of different cutting applications, such as somewhat variable cut depths, advances, cutting speeds, and workpieces. In order to increase the application possibilities of the cutter inserts and to better shape and get rid of the chips, German 3,148,535 suggests forming the chip-forming elements generally as truncated pyramids with generally triangular bases with at least one of the base-surface limiting lines being either parallel to the cutter edge or arranged on an arc relative thereto.
According to German 2,810,824 a one-sided cutter insert is proposed which has in the center of its upper side a raised portion which is shaped as a rectangle and has the basic shape of the cutter insert. The corners in particular of the square raised portion can be formed in the middle of the cutter, in particular annularly therearound. Cutter elements are also already known where the central chip breaker is formed as a chip-shaping step and the raised chip former extends to the cutter edge regions. The disadvantage of this embodiment is that cutting with high pressure leads to premature cutter-insert wear. In addition the quality of cut that is achieved is unsatisfactory.
Instead of the highly projecting chip-breaker steps in the corner regions one has used sphere segments or the like before the chip-breaker step and has changed these shapes partially into truncated cones or pyramids. The disadvantage of these cutter inserts that the surface geometry is difficult to produce with powder metallurgy since the chip-forming elements are of complicated shape, that can only be produced with great difficulty in a press. In addition it has been determined that the separate arrangement of the chip-forming elements in the corner regions leads to poor heat transfer which leads also to an increased wear of the cutter plate. In addition formation as an indexable cutter plate for such chip-forming elements is critical as they must serve for chip forming and also as support surfaces (after indexing).
In order to ensure a compensated good chip-forming relationship even with widely varying advances or cutting depths, it has further been suggested in European patent document 278,083 to provide on the chip surface at a right angle to the cutting edge on the bevel region a cutting angle of more than 30.degree. so that the cutting angle is smaller with increasing spacing from the bevel and to provide chip ribs projecting from the chip surface in the chip surface regions between the cutter-corner regions of the cutter body in the chip-movement direction and with lateral spacing from one another, between which further bumps with run-on ramps are provided. The corner regions have three adjacent stepped bumps including two outer ones with inclined axes parallel to the adjacent chip ribs. Even this cutter plate is only usable on one face since the chip breaker cannot form a sufficiently solid mounting surface.
European patent document 143,758 has longitudinally extending ridges which are trapezoidal in cross section and which extend parallel to the cutting edge. These ribs are interrupted by notches.
The prior-art cutter plates with chip-forming elements for producing coil chips have not worked.